1. Field of the Invention
The invention is directed to the field of subsurface boring with the use of high pressure fluid for the installation below ground of various utility items such as electrical cable, conduit, fluid-carrying pipes and ducts, gas lines, sewer pipes and the like.
2. Description of the Prior Art
The above-identified application discloses a drilling method and apparatus which departs from prior art techniques which are solely dependent upon fluid cutting for steering by utilizing fluid pressure to effect a positive action on the drill head to thereby direct the drilling head in the desired direction. By exceeding the predetermined fluid pressure determined by the dimensions of the fluid-conducting system, the drilling head is made to deflect from its normal position in the direction of desired movement of such drilling head. Such deflection of the drilling head is carried out while rotation of the drill string is terminated and once the deflection is completed, drilling is commenced in the new direction by the normal rotation and advancement of the drill string. Other prior art techniques for subsurface boring require that rotation of the drill string be stopped, the drilling head segments adjusted for a new direction of travel and rotation begin again. Such devices often use a beveled drill head, that is with one face of the drill head beveled in the direction of the longitudinal axis of the drill head or other wellknown drill head configurations.
The presence of hard materials such as rocks, hard soil, debris or conversely the presence of soft spots due to sand, wet soil, etc., may prevent the drilling head, whether according to the prior application of a prior-art beveled head or other well-known drilling heads, from getting a bite in the soil adjacent the end of the drilling head and cause it to drill in a direction offset from that desired based upon where the drill head gets a firm bite into the adjacent soil.